In recent, with the spread of digital cameras, the need of printing out color digital images has been increased. Various methods have been suggested for printing the color digital images. For example, thermal transfer printers, such as dye sublimation printers using a thermal head, can perform print representations by means of concentration gradation similar to conventional silver salt printers, so that printed matter extremely close to silver salt photographs can be obtained. Further, since they can be miniaturized without using liquids, such as chemicals, the thermal transfer printers have been paid attention to as printers providing silver salt photographs at home.
FIG. 1 shows a structural diagram of an important part of a thermal transfer color printer. The thermal transfer color printer comprises, as primary components, a thermal transfer ribbon 1, sheets 2, a platen drum 3, a thermal head 4, a clamper 5, a platen drum driving motor 6, a sheet hopper 7, a head lifting mechanism 19, etc. A friction member 8, such as rubber, is attached to a contact portion between the clamper 5 and a sheet 2.
In a transfer (or printing) area shown in FIG. 1, the thermal head 4, the thermal transfer ribbon 1, the sheet 2, and the platen drum 3 are arranged from an outer circumference side to an inner circumference side in a radial direction of the platen drum 3 such that the sheet 2 is sandwiched and held. The thermal transfer ribbon 1 is separated by color and is wound up such that a combination of a plurality of color materials periodically appears. For example, three colors of yellow, magenta, and cyan constitute a group. In addition to these colors, a ribbon to which black or a transparent overcoat material for coating a surface is added is prepared.
Now, a series of operations of the printer for forming a full color image on a sheet will be described with reference to an example using a three-color ribbon.
First, an arbitrary color of the thermal transfer ribbon 1 is cued. Next, the thermal head 4 is moved upward by means of the lifting mechanism 19 to be separated from the surface of the platen drum 3, and the sheet 2 is fed from the sheet hopper 7 by a sheet feed roller 18. The sheet 2 is guided by a sheet feed guide at an entrance, and is carried up to a position of the clamper 5 along the outer circumference of the platen drum 3. Next, the platen drum 3 and the clamper 5 apply insertion pressure to the carried sheet 2 to hold it. An underside surface, that is, a portion of the clamper 5 in contact with the sheet 2 is provided with the friction member 8, such as rubber, and holds the sheet 2 so as not to deviate (so as not to slip) from the platen drum 3. After the sheet 2 has been held, in order to keeping the thermal transfer ribbon 1 in close contact with the sheet 2, the head lifting mechanism 19 moves the thermal head 4 toward the platen drum 3 and to make close contact of the thermal head with the sheet 2.
Next, the driving motor 6 for the platen drum 3 is driven to rotate the platen drum 3, and thus moves the sheet 2 to be wound up on the platen drum 3. In synchronism with the movement of the sheet, electrical signals corresponding to an image having a first color are supplied to a minute heating element group of the thermal head 4 from a control unit (not shown). The minute heating elements generate heat corresponding to arbitrary dots constituting pixels of the image. Through this heating, the color material of the thermal transfer ribbon 1 is transferred to the sheet 2, and the image having a predetermined color is formed on the sheet 2.
After the first color transfer is finished, the head lifting mechanism 19 releases the pressing force of the thermal head 4 against the sheet 2, and moves the thermal head 4 to a separated position 4′ from the outer circumferential surface of the platen drum 3, so that the clamper 5 can pass therebetween. The platen drum 3 is rotated by means of the driving motor 6 to locate the front end of the sheet 2 at a predetermined position, and the thermal transfer ribbon 1 is reeled out to cue the next color.
Next, the driving motor 6 is driven to rotate the platen drum 3, so that the sheet 2 is rotated together with the platen drum 3. In synchronism with the rotatory movement of the sheet, electrical signals corresponding to a second color are supplied to the minute heating element group of the thermal head 4 from the control unit (not shown). The minute heating elements generate heat corresponding to arbitrary dots constituting pixels of the image. Through the heating, a second color material of the thermal transfer ribbon 1 is transferred onto the first color material, thereby forming an image having a mixed color of the first color and the second color on the sheet 2. In this way, by repeating the transfer process of color materials as many times as necessary colors, a color image is formed on the sheet 2.
However, conventionally, in order to prevent the slip of the sheet 2, the front end of the sheet 2 was held by the clamper 5. For this reason, as shown in FIG. 2, a large non-transfer (non-printing) area is generated in a section 2a of the sheet 2 between the clamper 5 and the thermal head 4, so that the transfer process cannot be performed to the entire surface of the sheet. The non-transfer area should be cut out later, so that a relatively expensive thermal transfer photograph sheet can be wasted. A positional deviation of a transfer position of the transfer image or a blur of the transfer image may be generated due to the contamination of the clamper 5 or depending upon the kind of a sheet.
Therefore, it is an object of the present invention to provide an image recording apparatus allowing a printing to be performed on the entire area of a sheet without an edge, as an image recording and output apparatus such for a digital camera, etc.
It is another object of the present invention to provide an image recording apparatus capable of suppress the generation of the slip of a recording medium due to the contamination or deterioration or abrasion of a friction member of a clamper, or depending upon the kind of the recording medium.